The diminished availability and high cost of hard woods for use as furniture or attractive building materials has proliferated the use of less expensive wood and wood composites. In many of these cases, the less expensive wood and wood composites are modified or finished such that they appear to be either natural wood or a specific hard wood. Generally, coatings may be applied to a wood or wood composite to provide a protective and/or decorative finish. The coatings may be in the form of a powder (e.g., dry, solventless) or solid solution. These coatings are known to provide a very durable finish.
In a powder coating process, a substrate to be coated can be heated to a specific temperature whereby a solid solution or powder coating may be applied to the surface of the substrate. The powder coating particles are electrically charged and ejected toward the substrate which is electrically grounded, providing an attractive electrostatic force that draws the particles to the substrate. The powdered substrate is heated once again to melt the powder. The resulting liquid flows out to form a continuous film over the surface of the substrate, and in some cases this additional thermal treatment cures the coating to provide a finished article. In those cases where this final heating step does not cure the coating, the coated article must be exposed to some other energy source such as ultraviolet light to cure the coating.
Generally, it is well known that wood and wood composites transmit an electrical ground via the moisture that is naturally present in the wood and wood composite substrate. In order to increase the conductivity of the wood and wood composite substrate, the substrate may be pre-heated prior to the application of the powder coating which forces water from the core of the substrate to the surface enhancing the electrostatic attraction between the substrate and the powder particles. However, it is very difficult to thermally control this migration of moisture without driving it entirely out of the substrate, typically resulting in poor powder coating uniformity and coverage of the article. Certain areas of a machined wood substrate such as edges formed at 90 degree angles and routed areas where large surface areas of highly porous substrate are exposed tend to dry out faster than the bulk areas of the substrate, leading to the condition of inadequate powder coverage and uniformity.
Accordingly, there is a need for a pre-treatment process that provides enhanced electrical conductivity of wood and wood composites prior to the application of a powder coating.